Take Matt Smith, the current Doctor in Doctor Who. He's 28. He looks 28, when you look at a photo of him, and in interviews when he's himself he often behaves 28. But his performance says "I'm 900+ years old, I'm wiser and crazier and more alien than any of you lot". It's in the eyes and the way he holds himself. Merely looking at what (I think) is a fabulous costume can't portray that - but I think Armitage could pull off the 195-year-old king in exile pretty well.